A radio protocol based on the 3rd Generation Partnership Project (3GPP) radio access network standard is divided into a first (L1) layer, a second (L2) layer, and a third (L3) layer based on the lower three layers of the Open System Interconnection (OSI) reference model. The second layer of the radio protocol includes a Medium Access Control (MAC) layer, a Radio Link Control (RLC) layer and a Packet Data Convergence Protocol (PDCP) layer. The third layer includes a Radio Resource Control (RRC) layer at the bottom of the third layer.
The RLC layer is responsible for guaranteeing Quality of Service (QoS) of each Radio Bearer (RB) and performing data transmission according to the QoS. The RLC layer includes one or two RLC entities for each RB in order to guarantee QoS specific to the RB. The RLC layer also provides three RLC modes, a Transparent Mode (TM), an Unacknowledged Mode (UM), and an Acknowledged Mode (AM), in order to support various QoS.
The PDCP layer is located above the RLC layer and can perform header compression on data transmitted using IP packets such as IPv4 or IPv6 packets. The PDCP layer is present only in a packet-switched domain and includes one PDCP entity per RB.
The RRC layer sets a variety of operating methods, parameters, and characteristics of channels associated with the first and second layers of the radio protocol in order to satisfy QoS. Specifically, the RRC layer determines which header compression method would be used at the PDCP layer and determines an operating mode, a RLC PDU size, and values of various protocol parameters which are used for the RLC layer.